Spondylolisthesis and Stability
Both views use the same technique as neutral lateral lumbars; 40" FFD, no
tube tilt, central ray aimed at the top of the iliac crest (works for both L4
and L5 spondylos), 90 kVp, whatever mAs is calculated for patient thickness.
You can use a smaller film (8" x 10") for this because you're only
interested in the listhetic area. Be certain to collimate to less than film
size. Specifics for positioning are given below.
TRACTION LATERAL LUMBAR
You need to have some type of hanging bar support situated so that the
patient can grab it and hang (remember monkey bars as a kid??). The toes can
just touch the ground so that the patient doesn't sway. I have the patient
perform this once quickly so that I can then determine the level of the film
and tube and then get everything set up. When the patient assumes the
position, produce the exposure as soon as possible.
COMPRESSION LATERAL LUMBAR
We use a standard backpack with about 50 pounds of sand inside. It goes on
both shoulders and we have the patient amble about the room for a couple of
minutes (we tried for 5 but that was too long). Use common sense here, don't
drop the pack on their shoulders. I don't think we've ever had someone that
couldn't tolerate the pack because of pain and we've had some ptosed
spondlyos. Position the patient and then produce the exposure.
The mensuration landmarks need to be visible on both traction and compression
films. Place a dot on the posteroinferior corner of the listhetic vertebrae,
another on the posterior edge of the vertebrae just inferior (prob the
sacrum) and another on the anterior edge of the inferior vert (sacrum again).
Connect the two lines on the inferior vertebrae then draw a perpendicular to
that line that passes through the posteroinferior dot of the listhetic
Three (3) mm change from traction to compression is defined as an unstable